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UNITED STATES PATENT OFFICE.

FRANK L. BARTLETT, OF PORTLAND, MAINE, ASSIGNOR TO THE AMERICAN ZINC LEAD COMPANY, OF SAME :PLAOE.

PAINT-PIGMENT.

SPECIFICATION forming part of Letters Patent No. 477,488, dated June 21, 1892. Application filed October 25, 1389. Serial No. 328,177. (Specimensd To all whom it may concern.- phuric acid, which would otherwise pass oil? Be it known that I, FRANK L. BARTLETT, a with the fumes. The fumes which are thus citizen of the United States, residing at Portcollected and which are the result of the first 50 land, in the county of Cumberland and State step of the process, consist, mainly, of zinc of Maine, have invented certain new and useoxide, lead sulphate, and zinc and lead sulf ulImprovements in Paint-Pigments, of which phites, with the sulphites of arsenic and other the following is a specification. volatile metals, sulphurous acid and carbon,

My invention relates to anew and improved and is of a dark-grayish color. This fume is 5 5 paint-pigment, which I have discovered and then placed in a furnace or retort out of conpractically manufactured. tact with the products of combustion and is Hitherto sublimed lead and zinc pigments heated to a low red heat, at the same time have been made by Various processes, but being gently and continuously stirred in the none have been made, so far as I am aware, presence of air and sulphurous gas for a conwhich would not change color on exposure to siderable length of time, (usually about thirty 15 the air, or harden and set when ground in linminutes) after which it is removed and alseed-oil. lowed to cool. By this last manipulation the In manufacturing this pigment I make use sulphurous acid, sulphites, arsenic, and other of low-grade refractory zinc ores which canloose sulphur compounds are driven off and not profitably be worked by the ordinary prozinc, lead, oxygen, and sulphur remain chemi- 2o cesses of smelting. An ordinary example of cally combined in the form of a dense white such ores contains from twenty percent. to homogeneous pigment orpowder having many forty per cent. of zinc, with from ten to fifteen of the characteristics of pure white lead, the ounces of silver. They also usually contain oxygen being in excess over and above what some gold and copper. The lead content is would be necessary to convert the metals into 25 below ten per cent, while the sulphur is prestheir oxides and the sulphur into sulphates. ent from twenty-five per cent. to forty per The pigment thus produced is perfectly cent. homogeneous in character, the elements being In manufacturing the pigment the raw sulunited in chemical combination and not in phuret ore is crushed and mixed with about the form of a mechanical mixture. This is 30 seventy-five per cent. of its weight of any kind shown bythe factthatwhen triturated in water of cheap fine coal or coal-culm, sawdust, peno separation of the lead and zinc can be troleum residuum,or the like, care beingtaken effected, and when allowed to settle through that the fuel is in a fine state of division and the water the upper portion contains the same that it contains some hydrocarbon. It is also percentage of lead as thelower. It is further 3 5 necessary that the amount of sulphur present shown by the fact that it cannot be imitated shall be equal to or in excess of the amount by any chemical process or by mixing two or of zinc. The ore is then burned in a suitable more elements. Neither can any mechanical furnace in the presence of an air-blast,wl1ich separation be effected, and the microscope is blown through the mass of ore and fuel fails to show anything but a homogeneous pro- 40 An air-blast is also introduced directly above duct.

the mass of ore. The zinc, lead, and other This pigment when ground in oil weighs volatile metals are thus sublimed and pass off nearly or quite as much as straight white in the form of a fume, which is collected in a lead. It will not settle or harden. It covers 0 bag-room or by any suitable means. The inas well and is as durable as the best white 5 troduction of the air-blast, as above described, lead of commerce. Like white lead it whitens immediately above the mass of ore results in on exposure, and unlike the sublimed lead keeping up the heat and destroying the sulhitherto made it does not turn yellow.

An analysis of a fair sample gives the fol-.

lowing result:

Zinc, metallic 7.33 Lead, metallic 24.92 Sulphur 2.06 Moisture, oxide of iron, soluble 'zinc sulphate .45 Oxygen 24.34 by dif.

Total 100.00

These proportions will be varied somewhat, according to the relative quantities of zinc, lead, and sulphur in the ore used.

In making the combinations of the elements as found above it will be seen at once that there is an excess of oxygen over what is required to combine with the sulphur to make sulphates and with the zinc to make zinc oxide. for this excepting We call the lead an oxysulphate-that is to say, sulphate of lead containing one equivalent of extra oxygen. This fact is further proved in this way: When pure There is no satisfactory way to account zinc ore free from lead is worked by the same process and made into zinc oxide, it invariably contains from seventy-eight per cent. to seventy-nine per cent. of metal, thus proving that the zinc is not the metal which holds the excess of oxygen. It is this excess of oxygen, as explained, which constitutes the peculiarity of my product and which seems to give to it its peculiar physical properties.

I claim- The herein-described pigment, consisting of a stable chemical compound having in combination zinc, lead, sulphur, and oxygen, and composed principally of zinc oxide and sulphate of lead, but having in combination a quantity of oxygen more than sufficient to form the said oxide and sulphate, substantially as described.

In testimony whereof I affix my signature in presence of two witnesses. 

